This invention relates to an improved combination expansion device and flow distributor unit for use in a reverse cycle (heat pump) air conditioning system.
A combination expansion device and flow distributor unit is disclosed in U.S. Pat. No. 4,643,222 which issued in the name of Wiser. A free floating piston is mounted within a housing which is arranged to close against the entrance of a passageway when refrigerant moves in one direction between a pair of multiple circuit heat exchangers. The piston contains a metering orifice through which refrigerant is throttled when the piston is in a closed position. The throttled refrigerant, which is in both the vapor phase and liquid phase, is discharged into an axially-aligned, drilled hole. A series of distributor channels are each passed at an acute angle into the distal end of the drilled hole. The axial length of the hole is extremely short and, as a consequence, the refrigerant vapor phase will not mix homogeneously with the vapor phase before the mixture enters the distributor channels. By the same token, because of the shallow entrance angle to the distributor channels, unequal amounts of refrigerant mixture can be discharged into each channel unless the flow directing surfaces are precisely machined. Accordingly, the performance of the individual downstream heat exchanger circuits will be adversely effected.
High precision distributors are available which are capable of more evenly distributing refrigerent into a multiple circuit heat exchanger. These devices, however, are relatively complex and expensive. Despite the use of precision parts, the distribution of refrigerant is oftentimes non-homogeneous and uneven. For the most part, these precision distributors are not applicable for use in reverse cycle systems.